Density and temperature study of the noncoincidence effect in liquid carbon disulfide

Solvent dependent frequency shift and Raman noncoincidence effect of S=O stretching mode of Dimethyl sulfoxide in liquid binary mixtures

The isotropic and anisotropic Raman peak frequencies of S=O stretching mode of Dimethyl sulfoxide (DMSO) have been discussed in different chemical and isotopic solvent molecules using different mechanisms. The shifting of peak frequency in further dilution of DMSO with solvent molecule is observed for all solvents. Transition dipole - transition dipole interaction and hydrogen bonding may play a major role in shifting of peak frequencies. The non-coincidence effect (NCE) of DMSO was determined for all the solvents and compared with four theoretical models such as McHale's model, Mirone's modification of McHale's model, Logan's model and Onsager-Fröhlich dielectric continuum model respectively. Most of the theoretical models are largely consistent with our experimental data.

Glass transition and fragility in the simple molecular glassformer CS(2) from CS(2)-S(2)Cl(2) solution studies

With an interest in finding the fragility for a simple, single component, molecular glassformer, we have determined the dielectric relaxation and glass transition behavior for a series of glasses in the CS(2)-S(2)Cl(2) and CS(2)-toluene systems. Crystallization of CS(2) can be completely avoided down to the composition 20 mol% second component, and the fragility proves almost independent of CS(2) content in each system. Since the glass temperature T(g) obtained from both thermal studies and from dielectric relaxation (using T(g,diel)=T(tau=100 s)) is quite linear over the whole composition range in each system, and since relaxation time data for pure CS(2) fall on the same master plot when scaled by the linearly extrapolated T(g) value, we deduce that pure CS(2) has the same high fragility as the binary solutions. The value is m=86, as for ortho-terphenyl (OTP). Based on observations of independent studies for the vibrational density of states (VDoS) (of inherent structures for OTP and instantaneous, at-temperature structures for CS(2)), we attribute the high fragility to an excess vibrational heat capacity (defined by C(p) (vib, excess)=dS(vib, excess)/d ln T) originating in the behavior of the low frequency modes of the VDoS (the boson peak modes). Both low frequency DoS and anharmonicity increase with increasing temperature, augmenting the configurational entropy drive to the top of the system energy landscape. The surprising implication is that fragility is determined in the vibrational, not configurational, manifold of microstates.